The present invention relates to a flat sensor for measuring temperature and/or expansion, to a special adaptation case for a sensor, to a use of a sensor, to an arrangement for compensating for thermal deformations using sensors, as well as to a method for performing the compensation.
European Patent No. EP 349 783 B1 discloses determining machine-tool temperatures in order to define their temperature-dependent expansion and to compensate therefor. The entire temperature variation over the expanding machine part is determined, in this context, for the temperature-dependent expansion. For this, one uses a resistor which extends in the direction of expansion of the machine part and features an intensive thermal contact with the machine part. The resistor used produces an output signal that is proportional to the average temperature and, thus, to the total expansion. For the contacting, suitable contact elements are provided at both ends of the resistor.
Here the drawback is that a separate resistor is needed for each required length. In addition, interference effects, such as deterioration due to ageing, which influence resistance and corrupt the measuring result, are not compensated.
The article,xe2x80x9cTemperatureinflxc3xcsse auf die Werkzeugmaschinen-Genauigkeitxe2x80x9d (The Effects of Temperature on Machine Tool Accuracy) by Reto Gruber and Wolfgang Knapp, published in xe2x80x9cWerkstatt und Betriebxe2x80x9d (Workshop and Operation), edition 131 (1998) 11, discloses that the warming of a machine tool results in deformations and, thus, in inaccuracies. Therefore, the new ISO/DIS 230-3 testing standard provides for determining thermal deformations in a machine tool to assess its accuracy. A warming of this kind essentially takes place during machine tool operation, in which, in particular, the spindle""s stationary mount heats up, the result being that the heat is conducted from there into the entire machine tool.
The above mentioned article merely discusses the problem and the test provided in ISO/DIS 230-3 for qualitatively determining thermal deformations.
An object of the present invention is to provide a sensor which avoids the mentioned disadvantages, and which can be used universally and produced cost-effectively. In addition, an aim is to provide a simple method for individually adapting the sensor to specific circumstances. Moreover, the present invention can provide a sensor arrangement for detecting a temperature distribution which causes a deformation in the machine tool, preferably using a minimum number of sensors. This arrangement should be able to be used universally and produced cost-effectively. In addition, the intention is to delineate a simple method for compensating for thermal deformations by utilizing the output signals from the arrangement.
The present invention provides a flat sensor for measuring temperature and/or expansion, in particular of a machine part, or of a length-measuring device or of an angular-position measuring device, comprising at least one structural component (ST1, ST2, ST3) having temperature-dependent electrical conductivity, the structural components (ST1, ST2, ST3) being uniformly distributed over the entire length of the sensor (S). The sensor is characterized in that at least two tracks (SP1, SP2, SP3, SP4, SP5, SP6), which include interconnected structural components (ST1, ST2, ST3), are provided.
Advantageous further features of the sensor may include that: (a) the structural components (ST3) of a track (SP5, SP6) are connected in series; (b) between the two structural components (ST3) is an electrical connection element (VE), which can be used to interconnect the two tracks (SP5, SP6); (c) a soldered point (LP) is provided as an electrical connection element (VE) for the two tracks; (d) the structural components (ST1, ST2) of one track (SP1, SP2, SP3, SP4) are connected in parallel; (e) the at least two tracks (SP1, SP2, SP3, SP4) are made up of at least two different materials; (f) an adhesive layer (KS) is provided on the rear side of the sensor (S) for adhesively mounting it on a component part to be measured, and that the adhesive layer (KS) is especially thermally conductive; (g) a protective layer is adhesively applied to the front side of the sensor (S) in its mounted state, protecting the sensor (S) from damage; (h) the sensor (S) contains electronic modules (V, AW); (i) the electronic modules contain an amplifier circuit (V); (j) the electronic modules contain an evaluation circuit (AW); (k) the sensor (S) has four tracks (SP1, SP2, SP3, SP4), the structural components (ST1) of the two tracks (SP1, SP4) being manufactured from a first material, and the structural components (ST2) of the two tracks (SP2, SP3) from a second material; and/or (1) the four tracks (SP1, SP2, SP3, SP4) in the evaluation circuit (AW) are interconnected into a bridge.
The present invention also provides a method for individually adapting a flat sensor, characterized in that a length of the sensor (S) that is no longer needed is cut along a trim line (SL) at the end of the sensor (S) which does not have any electronic modules (V, AW). Advantageously, the method may also provide that: (a) at the end of the sensor (S) which does not have any electronic modules (V, AW), the two tracks (SP5, SP6) are interconnected by electrical connection elements (VE, LP);(b) the sensor (S) is manufactured in the form of a long band, enabling the user to trim the long band to the required sensor length; and /or (c) the user connects electronic components (V, AW) to the sensor (S) via already existing connection elements (VE, LP).
The present invention further provides an application of the sensor characterized in that the sensor (S) is used for measuring an expansion, and that the longitudinal direction of the tracks (SP1, SP2, SP3, SP4, SP5, SP6) of the sensor (S) are arranged essentially orthogonally to the expansion to be measured.
The present invention also provides an arrangement for compensating for thermal deformations in machine tools using temperature sensors (7.1, 7.2, 7.3, 7.4) for measuring temperature at at least one machine part (3, 4, 5), characterized in that at those machine parts (3, 4, 5), which heat up during operation and which define the distance between the tool and the platen (1), temperature sensors (7.1, 7.2, 7.3, 7.4) are provided, and at those machine parts (3, 4) having a longitudinal extension, elongated temperature sensors (7.1, 7.2, 7.3) are provided, which are aligned in parallel to the expected deformation direction.
The arrangement advantageously may include that: (a) at least one point-shaped temperature sensor (7.4) is arranged at one stationary mount (5) of a spindle of the C-type machine tool; (b) at a cantilever arm (4) of the C-type machine tool, at least one elongated temperature sensor (7.4) is arranged in parallel to the Y-axis, which covers at least a large portion of the extent of the cantilever arm (4) in parallel to the Y-axis; (c) arranged at one frame (3) of the C-type machine tool, in parallel to the Z-axis, is it least one elongated temperature sensor (7.1, 7.2), which covers at least a large portion of the extent of the frame (3), in parallel to the Z-axis; (d) the temperature sensors (7.1, 7.2, 7.3, 7.4) are connected to the machine parts (3, 4, 5) via a connection featuring good thermal conductivity; (e) the temperature sensors (7.1, 7.2, 7.3, 7.4) are linked to an evaluation unit; and/or (f) a protective layer is applied to the temperature sensors (7.1, 7.2, 7.3, 7.4), protecting the temperature sensors (7.1, 7.2, 7.3, 7.4) from damage and from thermal irradiation.
The present invention provides yet further a method for compensating for thermal deformations on machine tools, in which average temperatures of the individual machine parts (3, 4, 5) are calculated from the output signals from the integrating temperature sensors (7.1, 7.2, 7.3); from the average temperatures, thermal deformations in the machine tool are calculated for each axis using linear equations; and compensation signals are produced for position control of the individual axes.
In accordance with the present invention, the sensor is made up of a plurality of tracks, each having interconnected structural components with temperature-dependent electrical conductivity. In this context, the different tracks are composed of at least two different materials, each of whose conductivity varies in its temperature dependence. In the case of a four-track sensor, it is also advantageous that, even in response to a linear deformation, no new adjustment is required in the evaluation electronics. The output signals from the sensor are independent of length.
A benefit of the method of the present invention is the fact that the parallel connection of the structural components results in the resistor elements being uniformly distributed, with temperature-dependent conductivity, over the entire length of the sensor, making it possible for the sensor to be trimmed quite easily to the required length. As a result, one attains the additional benefit that the temperature is advantageously measured over the entire sensor length.
In accordance with the present invention, the temperature-compensation arrangement is made up of a plurality of elongated temperature sensors, which are mounted on those machine tool parts which, in response to a deformation, effect a relative displacement between the tool and the workpiece of the machine tool. The elongated temperature-sensor structure enables one to determine and compensate for any deformation in the geometric dimensions of the machine tool caused by thermal deformation, merely by using a few temperature sensors, so that the operating result cannot be degraded by the temperature fluctuations. Due to the fact that the temperature distribution is integrated over the entire sensor surface, in those machine-tool components which cause a displacement between the workpiece and the tool, the displacement can be determined very precisely, without having to calculate complicated machine-tool and/or temperature-distribution models. It is advantageous that only simple linear calculations are needed to compensate for the thermal deformation. Using the elongated temperature sensor eliminates the need for considering the thermal distribution as a function of time. In addition, only one single temperature sensor is needed to measure the expansion of the machine tool""s cantilever arm.